Method and device for continuous production of glass-sheathed metal wires

ABSTRACT

The device and process allow for continuous processing of metal wire sheathed in glass ( 10 ) of considerable length.
         Normally a feed pipe ( 15 ) containing all the necessary metal, itself placed into a glass tube ( 20 ), so as to continuously supply a bead ( 14 ) to the lower part of the glass tube ( 20 ). Heat from a first inductor ( 23 ) around the glass tube ( 20 ) and a second inductor ( 24 ) under the glass tube ( 20 ) allow to maintain a bead ( 14 ) at a stable temperature and in a continuous manner and to obtain the continuous drawing process of a metal wire sheathed in glass ( 10 ).

FIELD OF THE INVENTION

This invention relates to the continuous processing of metal wiressheathed in glass, and in particular when the two constitutive materialsof the wire are heated and partially melted so as to be continuouslydrawn into their definitive shape.

Prior Art and Posed Problem

All of the prior art processes, for continuous processing of metal wiresheathed in glass, are based on an elaborate process described,initially, by Taylor in 1924. It consists of the following principle.

Firstly, a certain amount of metal is inserted into a glass tube closedat its base. The lower part of this tube is placed close to ahigh-frequency inductor, which results in the melting of the metalinside the glass tube. The glass softens through thermal conduction. Thecasting process of the microfilament, composed of a metal wire inside aglass tube, is manually initiated using a capillary tube. The initiatedwire is then placed on a revolving drum, so as to continuously draw thecomponent made of metal surrounded with glass. The wires, whose totaldiameter can vary between 6 and 25 μm, with a metal core varying from 2to 18 μm, are often obtained via this shaping process.

However, the main defect of this process is that it does not work in acontinuous manner, as, if the mass of metal inserted into the tube istoo great there is a risk of perforating the vitreous casing. Indeed,the coupling of the inductor with the metal is all the more importantthe greater the mass of the metal. Consequently, the importance of thesoftening of the lower part of the tube is directly dependent on themass of molten metal in this tube.

The mass of metal that can in inserted into the glass tube is thereforelimited, which forces the operator to split the casting process.

This inconvenience led to the development of this method. Thus, theRussian author's certificate, N^(o) 1 088 075, describes a castingprocess of a microfilament inside insulating glass, diagrammatized inFIG. 1. It uses a glass tube 1 in which a bead 5 is produced destined toconstitute the wire once the lower part of the glass tube 1 has softenedupon contact with this bead 5. A first inductor 4, placed around theglass tube 1, heats a metal rod 2, placed inside the glass tube 1, usingnose pliers 3, and lowered using a raising and lowering device 7. Theheating of the metal rod 2 is designed so that an input bead 8 of moltenmetal is constantly suspended from the lower part of the rod 2, so as toregularly supply the bead 5 placed in the lower part of the glass tube1, when it is being consumed too quickly. The lower inductor 6 allowsmaintaining the bead 5 in a molten state and thus carrying out thedrawing of the metal wire sheathed in glass.

If the process allows some of the problems posed by the Taylor processto be resolved, for example in providing a reservoir of metal, allowingto realise a considerably length of wire without stopping the machine,it nevertheless has two inconveniences linked to the discontinuation ofthe supply of molten metal to the micro-melt constituted by the bead 5and to the difficulty of controlling the input bead 8 at the lower endof the rod 2. Indeed, this input bead 8, of considerably mass comparedto the bead 5, creates a brutal increase of the mass of the metal bath,resulting in the drawing of the softened part of the glass tube 1, asfar as the zone with the highest magnetic intensity. The bath is thusbrutally brought to a very high temperature, which brings about a changein the geometric characteristics of the wire. Additionally, thediscontinuous melting of the rod 2, due to the several minute-longinterval separating the creation of the two successive input beads 8 atthe bottom of the rod, generates a periodic supply of non-homogeneousoxides in the bead 5, prejudicial to the homogeneity of the qualities ofthe metal wire. Indeed, some of these oxides whose melting point ishigher will form inclusions often insoluble, which, brought into themetal wire creation zone, risk fracturing it.

Another solution is presented in the U.S. Pat. No. 3,362,803. Itconsists in filling the glass tube with the necessary amount of metalfor the required length of metal wire, but then by melting only themetal at the lower part of the glass tube via induction. The upper partof the metal is pre-heated via an electric resistance to a temperaturelower than that which would soften the glass or ceramic, but as themolten metal is a good heat conductor, the heat will propagate upwards.The glass, being in contact with the molten alloy, will soften at aheight such that there will be a risk of breaking the glass tube due tothe action of the mass of the molten metal contained therein.

The purpose of this invention is to resolve the problems posed by thedevices and processes mentioned above.

On the other hand, through the documents of patent U.S. Pat. No.3,481,390, a process is known allowing to work metals with a highmelting temperature, which render the glass overly liquid, and ofreactive metals which limit the type of materials that can be used toconstitute the device. The process proposed in this document consists inmelting the metal/metal alloy in a refractory crucible, totally inertcompared to the latter. This crucible, whose base ends in a die, isplaced into the glass tube, without coming into contact with it. A firstmeans of heating are used to melt the alloy contained in the crucibleand a second means are placed near the lower part of the glass tube tosoften it, so as to initiate a glass capillary, from the latter. On theother hand, the device uses means allowing a pressure to be applied inthe crucible to eject the liquid alloy through the orifice of the die,in the form of a stream of molten metal, in the direction of the mouldedcapillary. In this device, the metal coming out of the crucible fallsbetween 2 and 15 cm, to reach, as late as possible, the glass tube, themetal having cooled down slightly. The contact between the molten metaland the glass last a very short time (contact time between 0.5 and 0.002s) and solely on the capillary. Consequently, the process, implementedin document U.S. Pat. No. 3,481,390, is very different to the Taylorprinciple (no permanent beads, use of over pressure to eject the moltenmetal). Additionally, the wire obtained through the process implementedin this document generally has a diameter greater than 30 μm, while oneof the purposes of the invention is to produce, at high speed, wire witha diameter less than 20 μm (speed greater than 10 m/s).

SUMMARY OF THE INVENTION

A first main objective of the invention is a continuous processing ofmetal wire sheathed in glass consisting in:

-   -   inserting metal into a glass tube, which is movable;    -   heating the metal until it melts inside the glass tube, so as to        create a bead, thus allowing to soften the lower part of the        glass tube; and    -   drawing in a continuous manner the assembly comprising molten        metal surrounded in glass, which came from the lower part of the        glass tube, whilst slowly lowering the glass tube, as it is        consumed through the drawing of the obtained sheathed wire.

According to the invention, a heat resistant feed pipe is used, which isimmovable in respect to the glass tube and has an external diameter lessthan the internal diameter of the glass tube, being totally inert asregards the metal mass and not softening at the temperature the metalmass reaches, being placed inside the glass tube, filled with all of themetal needed to process a large quantity of metal wire sheathed in glassand bored with a nozzle at its lower part, this nozzle being at a setminor distance from the lower part of the glass tube, in contact withthe proceeding bead, thus allowing the formation of the proceeding beadand the continuous supply of the latter, so that the dimensions of thisproceeding be ad remain substantially constant during the drawing of thewire. Means of applying negative pressure on the feed pipe are used toretain the molten metal mass in the tube. The negative pressure is thenreleased and regulated so as to provoke the start of the flowing of themolten metal via the nozzle and to control the continuous flow of themetal mass throughout the drawing.

It proved advantageous to flush an inert gas such as argon between thetwo tubes to minimise the quantity of oxides in the processed wire.

It is very beneficial to use these means (aforementioned gas flushing)to flush out and drain the inside of the feed pipe with an inert gas,prior to the melting of the bead.

A second main objective of the invention is a device for continuousprocessing of metal wire sheathed in glass, comprising:

-   -   a glass tube closed at its base, of set diameter, and    -   means of heating to melt a metal mass placed inside the glass        tube and to maintain a proceeding bead in a liquid state        softening the lower part of the glass tube.

According to the invention, it comprises a feed pipe containing themetal mass, of an external diameter less than the internal diameter ofthe glass tube that does not soften at the operating temperature, thisfeed pipe, with a nozzle at its lower part, being placed inside theglass tube so as to place its nozzle very close to the glass tube;

-   -   means of moving the glass tube to make it progressively descend        as it is consumed through the drawing of the wire; and    -   means of applying negative pressure and flushing to create and        manage a negative pressure on the inside of the feed pipe, so as        to regulate and control the flow of the molten metal mass        feeding the proceeding bead.

In the preferred embodiment of the means of heating, the latter comprisea first induction furnace whose coils surround the lower part of thefeed pipe by several centimeters.

Preferably, that the means of heating the proceeding bead inside theglass tube comprise a second inductor, in the shape of a shell andplaced below the lower part of the glass tube.

A circulation of argon is organised between the glass tube and the metalfeed pipe and a cable gland joint is used at the upper part of the glasstube to create a leak-proof joint between it and the metal feed pipe.

The device is completed via means of flushing using an inert gas in theglass tube.

LIST OF FIGURES

The invention and its different characteristics will be betterunderstood upon reading the following detailed description, along withthe two figures which respectively represent:

FIG. 1, already described, a device according to prior art; and

FIG. 2, a device according to the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

In reference to FIG. 2, the device according to the invention uses theoperational elements described in FIG. 1 and relative to the prior art.These are the glass tube 20, a first heating element comprised of aninductor 23, placed around the latter, a second means of heatingcomprised of a second inductor 24, placed under the lower part 21 of theglass tube 20, and means of flushing and applying negative pressure 38inside the tube 15. To better explain the manufacturing process of metalwire sheathed in glass, the following secondary elements have beenincluded in FIG. 2.

Temperature sensors, such as pyrometers 30 are placed next to the meansof heating the glass tube 20 and next to the means of heating its lowerpart 21. A water jet device 34 sprays the sheathed metal wire 10 issuingfrom the drawing to rapidly cool it down. A wire diameter-measuringdevice 31 is placed downstream to the unit to control the diameter ofthe wire. Finally, a winding device 11, in the shape of a coil, storesthe thus drawn 10 wire.

Depending on the melting temperature of metal alloys used to process thesheathed metal wire 10, different types of glass can be used to createthe tube 20, such as borosilicate, aluminosilicate, silica at 96% ormelted quartz glass. Ceramics can also be used. Additionally, the factthat the drawing temperature is 50 to 300° C. greater than that of themelting point of the metal must be taken into account. A progressivelowering device 25 allows the glass tube 20 to be gently lowered, as itis consumed through the drawing of the wire.

A major technical characteristic of the invention therefore consists inusing a feed pipe 15 into which is placed, beforehand, all the metalmass 12 composed of metal or metal alloy. This feed pipe 15 can becomposed of a refractory material, whose breakdown or deteriorationtemperature is greater than the operating temperature. It could be ofquartz, for example, when it is desired to create amorphous ormicro-crystallised alloys whose melting temperature is around 1,000° C.For alloys whose melting temperatures are higher it is possible to usealumina, boron nitride or titanium boride pipes.

This feed pipe 15, which is immovable, is therefore filled with thealloy or metal to be shaped otherwise unalloyed elements constituting analloy. The metal mass 12 is brought to melting point by the coils of afirst inductor 23 comprising a part of the means of heating. Indeed, thelatter surrounds the feed pipe 15 at its lower part, thus creating asecond heating zone, compared to the one in the device of FIG. 1,symbolising the prior art. The number of coils of the first inductor 23depends on the height of the molten metal of the metal mass 12 that isdesired to be obtained.

The inert gas flushing and negative pressure and flushing device 38 istherefore directly connected to an outlet above the feed pipe 15 toavoid, once the metal mass 12 has melted, the latter freely flowingthrough the lower nozzle 13 of the feed pipe 15. This lower nozzle isplaced just above the lower part 21 of the glass tube 20. It is to benoted that the latter is also placed in relation to the second inductor24, which is placed just below the lower part 21 of the glass tube 20,so as to adequately bring the proceeding bead 14 and the glass of theglass tube 20 to the appropriate temperature for drawing. The height ofthe nozzle 13, with regard to the lower part 21 of the glass tube 20, islower than or level with the desired height of the bead 14, designated“proceeding bead” in the proceeding zone which is between the nozzle 13of the feed pipe 15 and the lower part 21 of the glass tube 20. Theheight of the proceeding bead 14 sets the temperature range at the baseof the glass tube 20 and the force applied by the weight of theproceeding bead 14 to the lower part 21 of the glass tube 20. In usingthe negative pressure and flushing device 38 it is possible to controlthe height of the proceeding bead 14. Additionally, in setting thetemperature of the metal mass 12 in the feed pipe 15 to a value close tothe temperature of the proceeding bead 14 any thermal imbalance will beavoided in the proceeding zone which is that of the proceeding bead 14.

It is also to be made clear that not only the mass and temperature ofthe proceeding bead 14 but also its shape influences the geometry andthe qualities of the obtained sheathed wire. In the processes of theprior art, the metal in the glass tube essentially has the shape of aproceeding bead resembling an oblate spheroid. Through the use of a feedpipe 15 it is possible to control the shape of the proceeding bead 14,in particular the area in contact with the lower part 21 of the glasstube 20. For this purpose, the nozzle 13 can have several differentshapes so as to obtain different results.

It is to be noted that, as the supply of molten metal is via a directmeans in the proceeding zone, the possible presence of dross or moltenglass floating on the surface of the proceeding bead 14 is of noconsequence.

The second inductor 24, comprising the means of heating the proceedingbead 14 and placed under the lower part 21 of the glass tube 20, iscomprised of one or several inductor coils. This second inductor 24 isplaced next to the proceeding bead 14, preferably just below the lowerpart 21 of the glass tube 20, so as to maintain the proceeding bead 14in sustenance, thanks to the buckling forces.

Thus, in the embodiment of FIG. 2, a flat, slightly curved, in the shapeof a shell with a hole bored in its centre, the edges being raised fromthe central hole 26, single coil is used. The glass tube 20 is placed upto 10 mm above the central hole 26. In particular, the central hole 26is located under the glass tube 20, its inside radius can be less thanthe radius of the glass tube 20. This allows to reduce the height ofheating which is about the same as the inside radius of the coil. Theheating energy is therefore concentrated on the proceeding bead 14.

The second inductor 24 can also be composed of several coils with aconical layout also allowing to carry out the sustenance of theproceeding bead 14. This sustenance implementation allows to avoid asudden elongation of the glass tube 20, by reducing the force applied tothe lower part 21 of the glass tube 20.

An infrared radiation furnace can also be used to constitute these meansof heating the proceeding bead 14.

The inlet feeder 32A and the outlet feeder 32B allow to organise acirculation of argon between the glass tube 20 and the outside of thefeed pipe 15. The sealing of this area is ensured by a cable gland joint33 placed between the glass tube 20 and the feed pipe 15.

Remember that the glass tube 20 is movable compared to the feed pipe 15and compared to the two inductors 23 and 24. In this way, as it isconsumed through the drawing of the wire, the glass tube 20 is slowlylowered.

The process according to the invention is as follows.

All of the metal or metal alloy needed to process the sheathed wire 10is inserted into the feed pipe 15, in the shape of ingots or powder.This metal mass 12 is heated by the first inductor 23 and melted insidethe feed pipe 15.

Beforehand, the device is drained and pressurised with inert gas, inparticular argon, prior to the melting of the metal. Thus, a flow ofargon circulates in the feed pipe 15 towards the glass tube 20, thanksto the means of applying flushing and negative pressure 38 and to theinlet 32A and outlet 32B feeder. The nozzle 13 of the feed pipe 15 isnot as yet obstructed by the molten metal.

The first inductor 23 heats the metal mass 12 and the flow of argon inthe feed pipe 15 is stopped. Then, a negative pressure is created insidethe feed pipe 15 to stop the molten metal mass 12 from freely flowingtowards the lower part 21 of the glass tube 20. On the other hand, theargon flushing is still ensured inside the glass tube 20 and outside thefeed pipe 15 thanks to the argon inlet 32A and outlet 32B feeders.

The negative pressure inside the feed pipe 15 is then reduced to allowthe slow and continuous flow of the liquid metal mass 12 towards thelower part 21 of the glass tube 20, and this with a set flow rate ofmolten metal. The proceeding bead 14 then forms inside at the lower part21 of the glass tube 20 whose dimensions and mass are controlled. Thelatter is, moreover, heated and maintained in a liquid state by thesecond inductor 24.

The supply process must progress without any dynamic disturbance. On theother hand, the metal mass of the proceeding bead 14 must not be toogreat so as to avoid excessive drawing of the softened glass of thelower part 21.

The mass of the proceeding bead 14 must be kept stable. Thus, thequantity of consumed metal through the drawing of the wire is constantlybeing replaced by the same quantity of metal coming from the feed pipe15.

The temperatures of the molten metal mass 12 and of the proceeding bead14 must be very close, so as to limit as much as possible the thermaldisturbance.

It is thus possible to continuously process metal wire by introducingforty or so grams of CoFeNiMoSiB alloy into the feed pipe 15 made inquartz. The glass tube 20 can be made in borosilicate of type PYREX 7740.

The second inductor 24 is a slightly curved single coil of 50 mm indiameter, bored with a hole 26 of 8 mm in diameter. The first inductor23 can be composed of several coils of 20 mm in diameter over a heightof 100 mm. This must be placed 20 mm above the second inductor 24,itself placed 10 mm below the lower part 21 of the glass tube 20.

The height of the glass tube 20 can be 500 mm, its inside diameter being12.6 mm and the thickness of its wall being 1.2 mm.

The feed pipe 15 can be nearly 1 m high, with an outside diameter of 10mm and an inside diameter of 8 mm. The nozzle 13 located at its lowerpart can be 1 mm in diameter. Of course, this feed pipe 15 is centredinside the glass tube 20 and positioned 10 mm above the lower part 21.

In this case, the temperature of the metal alloy is maintained at about1,280° C. in the pipe 15 and tube 20. This temperature is controlled bytwo pyrometers 30. The mass of the proceeding bead 14 is about 5 g andits height about 10 mm.

The feeding rate of the glass tube 20 is set at 2.5 mm/min, the reelingrate at 10 m/s. The down speed of the level of molten metal mass 12 inthe feed pipe 15 is 0.2 mm/min.

The drawn wire under these experimental conditions has a total diameterof 16 μm and a metal core of 5 μm.

In the same way, twenty or so grams of CoFeNbB alloy can be insertedinto the feed pipe 15 with a total diameter of 8 mm and an insidediameter of 6 mm. The temperature of the metal alloy is maintained at1,260° C. in the pipe 15 and tube 20. The feeding rate of the glass tube20 is set at 2 mm/min, the reeling rate at 18 m/s. The down speed of thelevel of molten metal mass 12 in the feed pipe 15 is 0.75 mm/min.

The drawn wire under these conditions has a total diameter of 10 μm anda metal core of 5 μm. The reeling rate can be increased to valuesranging from 20 to 80 m/s, on the basis that the down speed of the pipeis increased from 4 to 13 mm/min. For example, a wire with a totaldiameter of 9 μm and a metal core of 4 μm can be obtained.

In all cases, upon exiting the second inductor 24, the sheathed metalwire is drawn and then soaked by the water jet 35, thus giving it anamorphous structure.

The unit is fitted with a laser diffraction sensor 31, placed 300 mmbelow the second inductor 24. It allows the total diameter of theprocessed sheathed wire to be measured throughout the drawing process.

1. A method for continuous processing of a metal wire sheathed in glass(10), comprising the steps of: inserting metal (12) into a glass tube(20); heating the metal until the metal melts inside the glass tube(20), at a lower part of the glass tube (20), so as to create aproceeding bead (14) at the lower part (21) of the glass tube (20) so asto soften the lower part of the glass tube (20); and drawing in acontinuous manner an assembly comprising molten metal surrounded inglass, which came from the lower part (21) of the glass tube (20),whilst slowly lowering the glass tube (20) partially melted at the levelof the lower part (21), as the glass tube (20) is consumed through thedrawing of the obtained glass sheathed wire, characterised in that aheat resistant feed pipe (15) including an external diameter less thanthe internal diameter of the glass tube (20) is placed inside the glasstube (20) and filled with all of the metal needed to process a quantityof metal wire sheathed in glass (10), wherein the feed pipe (15) isinert as regards to the metal and includes a nozzle (13) at a lower partof the feed pine (15), wherein the nozzle (13) is positioned at a setdistance from the lower part (21) of the glass tube (20) and in contactwith the proceeding bead (14), thus allowing the formation of theproceeding bead (14) and permitting the dimensions of the proceedingbead (14) to remain substantially constant during the drawing of thewire, and using means of applying negative pressure within the feed pipe(15) to retain the metal (12) in the feed pipe (15), and then to releaseand regulate the negative pressure within the feed pipe (15) so as toprovoke the start of the flowing of molten metal via the nozzle (13) andto control the continuous flow of the metal (12) throughout the drawingof the assembly.
 2. The method according to claim 1, further comprisingthe step of circulating an inert gas between the feed pipe (15) and theglass tube (20).
 3. The method according to claim 1, wherein the meansof applying negative pressure is used to flush out inert gas inside thefeed pipe (15) prior to melting the metal (12) in the feed pipe (15). 4.A device for continuous processing of a metal wire sheathed in glass(10), the device comprising: a glass tube (20) closed at a lower part(21); means of heating (23) to melt a metal mass (12) placed inside theglass tube (20) and to maintain a proceeding bead (14) in a liquid statesoftening the lower part (21) of the glass tube (20); a feed pipe (15)containing the metal mass (12) and including an external diameter thatis less than an internal diameter of the glass tube (20), wherein thefeed pipe (15) is configured such that the feed pipe (15) does notsoften at the melting temperature of the metal mass (12), the feed pipe(15) including a nozzle (13) at a lower part of the feed pipe (15),wherein the feed pipe (15) is placed inside the glass tube (20) suchthat the nozzle (13) is positioned adjacent the lower part (21) of theglass tube (20); means of moving the glass tube (20) to make the glasstube (20) progressively descend as the glass tube (20) is consumedthrough a drawing of the wire; and means of applying negative pressureto the feed pipe (15) to create and manage a negative pressure withinthe feed pipe (15), so as to regulate and control the flow of a moltenpart of the metal mass (12).
 5. The device according to claim 4, whereinthe means of heating includes a first inductor (23) to heat the insideof the feed pipe (15) at the lower part of the feed pipe (15), overseveral centimeters of the feed pipe (15), thus constituting a firstinduction furnace.
 6. The device according to claim 4, wherein the meansof heating includes a second inductor (24), in the shape of a shell andplaced below the lower part (21) of the glass tube (20).
 7. The deviceaccording to claim 4, wherein the device is configured to circulateargon (32A, 32B) between the glass tube (20) and the feed pipe (15), thedevice further including a cable gland joint at an upper part of theglass tube (20) to create a leak-proof joint between the glass tube (20)and the feed pipe (15).
 8. The device according to claim 7, furthercomprising means of flushing the glass tube (20) with an inert gas (32A,32B).